Hmm... excuse me, but i think it is neither a reason of the Delphi-Bridge, nor of the programming langaue. Because in debug mode (=the debug mode of IA, hope this has been clear to you) the plugin is being called by IA.

from personal experience in plug-in development, I never used IA in debug mode to debug my plug-in code.I always use the integrated Visual Studio debugger with c++. In my case is native code and very pobably you can't do the the same with c#.

Anyway, if your plug-in is not called at all you should receive an error during the setup package execution.Also check if the plugin runtime (the dll) is placed under TEMP folder of your package when you execute it.